FIG. 6 shows a hydraulic excavator as an example of construction machine 1 equipped with a crawler type traveling unit 2 which includes a speed reducer having a sprocket 3 provided with bearings shown in FIG. 7. Two tapered roller bearings are used, each having: an inner ring 4; an outer ring 5; a plurality of rolling elements 6 between the two rings; and a retainer 7 holding the rolling elements 6. The two tapered roller bearings are aligned with their smaller flanges of the inner rings 4 facing each other. Also, the bearings are axially positioned by a holding plate 12.
In this sprocket bearing, the outer ring 5 is fixed to a sprocket housing 8, and rotates integrally with the sprocket housing 8.
On the other hand, the inner ring 4 of the sprocket bearing is fixed to a motor housing 9 which does not rotate.
The sprocket has sealing function to keep internal lubricant and to prevent external soil from entering.
Conventionally, a floating seal 10, which is a separate member from the bearing, is used for the sprocket bearing (Patent Literature 1).
This floating seal 10 makes use of two rubber members 10a for establishing elastic contact of a seal ring 10b thereby holding internal lubricant.